Inkjet printing mechanisms use moveable cartridges, also called pens, that use one or more printheads formed with very small nozzles through which drops of liquid ink (i.e., dissolved colorants or pigments dispersed in a solvent) are fired. To print an image, the carriage traverses over the surface of the print medium, and the ink ejection elements associated with the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller. The pattern of pixels on the print media resulting from the firing of ink drops results in the printed image.
During printing, ink aerosol can be generated. The aerosol is composed of minute ink particles or satellites that become detached from a main ink droplet. Aerosol drops can make printers dirty, stain the output, and even hurt functionality by coating internal printing operating parts such as encoder strips or sensors.
There are several occasions beyond normal printing where aerosol can occur. For example, aerosol can occur during tube purging, printhead start-up, printhead servicing, drop detection, setting the thermal turn on voltage (TTOV), and printing alignment marks, spit strips, or fiducials that are eventually cut off a page. There are also certain printer operations, such as overprinting and underprinting black ink with color, when the printing conditions are somewhat arbitrary.
The effect of aerosol tends to be more pronounced during servicing than during printing. Printhead servicing generally includes a process known as “spitting.” Spitting is the ejection of non-printing ink drops into a spittoon within the service station. During spitting, the typical spittoon target area is farther from the printhead than is the print media during printing. For example, during normal printing, the printhead is usually spaced approximately one millimeter (1 mm) above the print media. When spitting, an ink drop from may need to travel a distance greater than five millimeters (>5 mm) to reach the spittoon target surface. Such an increased distance tends to create more aerosol.
In order to reduce inkjet aerosol, various methods have been used. These include modifying physical components such as spittoons and absorbers to try and catch more aerosol. This has been profitable in some cases, but has not completely eliminated the problem of contamination by aerosol. Other solutions, such as forced ventilation provided by one or more fans, have been tried. However, this has resulted in an increase both in manufacturing costs (e.g., due to increased complexity of the printer) and operational costs (e.g., due to increased electricity consumption) of printers.